As shown in FIG. 1, a rotary regenerative air preheater (hereinafter referred to as the “preheater”) is generally designated by the numeral 10. The preheater 10 includes a rotor assembly 12 rotatably mounted on a rotor post 16. The rotor assembly 12 is positioned in and rotates relative to a housing 14. For example, the rotor assembly 12 is rotatable about an axis A of the rotor post 16 in the direction indicated by the arrow R. The rotor assembly 12 includes partitions 18 (e.g., diaphragms) extending radially from the rotor post 16 to an outer periphery of the rotor assembly 12. Adjacent pairs of the partitions 18 define respective compartments 20 for receiving a heat transfer assembly 1000. Each of the heat transfer assemblies 1000 include a plurality of heat transfer sheets 100 and/or 200 stacked upon one another.
As shown in FIG. 1, preheater 10 is a bisector configuration in which the housing 14 includes a flue gas inlet duct 22 and a flue gas outlet duct 24 for channeling the flow of heated flue gases through the preheater 10. The housing 14 further includes an air inlet duct 26 and an air outlet duct 28 for channeling the flow of combustion air through the preheater 10. The preheater 10 includes an upper sector plate 30A extending across the housing 14 adjacent to an upper face of the rotor assembly 12. The preheater 10 includes a lower sector plate 30B extending across the housing 14 adjacent to lower face of the rotor assembly 12. The upper sector plate 30A extends between and is joined to the flue gas inlet duct 22 and the air outlet duct 28. The lower sector plate 30B extends between and is joined to the flue gas outlet duct 24 and the air inlet duct 26. The upper and lower sector plates 30A and 30B, respectively, are joined to one another by a circumferential plate 30C. The upper sector plate 30A and the lower sector plate 30B divide the preheater 10 into an air sector 32 and a gas sector 34.
As illustrated in FIG. 1, the arrows marked ‘A’ indicate the direction of a flue gas stream 36 through the gas sector 34 of the rotor assembly 12. The arrows marked ‘B’ indicate the direction of a combustion air stream 38 through the air sector 32 of the rotor assembly 12. The flue gas stream 36 enters through the flue gas inlet duct 22 and transfers heat to the heat transfer assembly 1000 mounted in the compartments 20. The heated heat transfer assembly 1000 is rotated into the air sector 32 of the preheater 10. Heat stored in the heat transfer assembly 1000 is then transferred to the combustion air stream 38 entering through the air inlet duct 26. Thus, the heat absorbed from the hot flue gas stream 36 entering into the preheater 10 is utilized for heating the heat transfer assemblies 1000, which in turn heats the combustion air stream 38 entering the preheater 10.
As shown in FIG. 2, a prior art seal 40 extends axially from (i.e., parallel to the axis A) and radially along an edge of each of the diaphragms 18 towards the sector plate 30A. Another seal 40 extends axially from and radially along an opposite side of each of the diaphragms 18 towards the sector plate 30B (only one seal 40 shown in FIG. 1). The seal 40 typically includes a flexible seal leaf 42 having a base portion 42B that is positioned between an L-shaped backing bar 43 and an elongate holding bar 41. A base portion 41B of the holding bar 41, the base portion 42B of the flexible seal 42 and a base portion 43B of the backing bar 43 are secured by a plurality of bolts 45 and nuts 46 between a spacer bar 44 and the diaphragm 18, radially along a length of the diaphragm 18.
During operation of the preheater 10, a surface 31′ of the sector plates 30A and 30B is spaced apart from a distal end of the seal 40. However, during start-up conditions when the preheater 10 and ducts 22, 24, 26 and 28 are relatively cold, the surface 31 of the sector plates 30A and 30B slidingly engage the respective seal 40. Such sliding engagement causes the flexible seal leaf 42 to wear and results in bypass leakage between the air sector 32 and the gas sector 34. In addition, through laboratory testing, the inventors have surprisingly found that such sliding engagement of the seal 40 with the respective sector plate 30A and 30B results in oscillatory vibration of the seal 40, as indicated by the arrow V, causing fatigue failure thereof. In addition, the inventors have discovered that because the seal 40 is mounted on a leading edge of the diaphragm 18, the edge of the diaphragm 18 acts as an abrupt fulcrum 47 upon which the seal 40 is bent over and causes stress concentrations at the mating portion of the seal 40. Such stress concentrations cause premature failure of the seal 40.
In addition, International Publication No. WO 97/37186 A1 discloses an arrangement in an air preheater for maintaining a controlled gap between a flexible sealing member and a sector plate at full load operating conditions to reduce leakage and sealing surface wear; and to provide a means to eliminating gapping between the sealing surface and the flexible sealing member in an air preheater due to deflection caused by gas pressure differentials, means for preventing premature failure due to edge fracturing of the flexible sealing member, and means for eliminating gaps between adjacent segments of the flexible sealing member.
Japanese Patent Application No. S59 231396 A discloses a front plate is detachably attached to an upper selector plate. An elastic thin plate sealing member is detachably attached on a back portion of the front plate 6. The back plate is detachably attached on the back portion of the elastic thin plate sealing member so that the deformation curvature of the elastic thin plate sealing member is limited.
U.S. Patent Application Publication No. US 2013/105105 A1 discloses a bimetallic seal for an air heater to flex and close a gap as the temperature changes using a laminated metal/bimetallic seal that deflects to provide a seal to control leakage.